The only application I have on my Mac that works with PhotoStream is iPhoto. I'm wondering if my Mac grabs the images from PhotoStream constantly or if it only downloads them when I launch an application that uses PhotoStream (such as iPhoto).

2 Answers
2

Yes! A process called PhotoStreamAgent runs at login, and idles in the background, downloading new photos when they're uploaded to your Photo Stream.

There exist both /Applications/Aperture.app/Contents/Library/LoginItems/PhotoStreamAgent.app and /Applications/iPhoto.app/Contents/Library/LoginItems/PhotoStreamAgent.app, indicating that this background-downloading behavior works no matter which application you use to manage your photo library.

This is also why iCloud in System Preferences also requires you to have one of the two installed, instead of it being installed in /System/Library/ or the like.
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jmlumpkinMar 23 '12 at 21:53

That's good to know, but I assume that ~/Library/Application Support/iLifeAssetManagement/assets only stores the Photo Stream photos (as opposed to photos contained in your iPhoto library) - which are limited to the most recent 1000. Say you don't start iPhoto for a long time, and you've snapped more than 1000 photos in the meantime: would you then miss out on some of the photos? Or do the agents perform ongoing imports from that location?
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mklement0Oct 4 '13 at 23:53